The Hawaiian Islands trigger an extraordinary interaction
between wind and ocean that extends thousands of kilometers.
This island effect is much larger than has ever been observed
by scientists before.

Using data from Earth-observing satellites, researchers
discovered this unusually long island "wake," which includes a
narrow eastward-flowing ocean current extending 8,000
kilometers (4,900 miles) from Asia to Hawaii. The scientists'
report appears in the June 15 issue of the journal Science.

While scientists have known of an eastward current off of
Asia for some years, this new research shows that it extends
from Asia to the Hawaiian Isles. Some researchers say such a
current could possibly have aided the islands' early settlers.

"Our study shows how tiny islands, barely visible on a
world map, can affect a long stretch of Earth's largest ocean.
The Pacific could only be sketchily observed with ship-based
instruments; advanced satellite technology, however, is
changing all this and giving us fascinating new images of this
ocean," said author Dr. Shang-Ping Xie, from the University of
Hawaii's International Pacific Research Center and Meteorology
Department.

"According to conventional theories and observations, the
wind wakes caused by islands should dissipate within
approximately 300 kilometers (180 miles) downstream and should
not be felt in the western Pacific," said co-author Dr.
Timothy Liu of NASA's Jet Propulsion Laboratory, Pasadena,
Calif. "But we were able to observe a pattern that stretches
more than 3,000 kilometers (1,800 miles) in the atmosphere and
the ocean from the western side of the Hawaiian Islands to
beyond Wake Island in the western Pacific. This pattern, never
recognized before, is a narrow but long break in the steady
Pacific trade winds and the North Equatorial Current. It is
triggered by the high Hawaiian Islands and sustained by
positive ocean-atmosphere feedback."

In their paper, "Far-Reaching Effects of the Hawaiian
Islands on the Pacific Ocean-Atmosphere," the authors describe
a chain of events that begins when the steady westward trade
winds and north equatorial current encounter the volcanically
formed Hawaiian Islands standing tall in the middle of the
Pacific Ocean. The islands force the winds to split, creating
areas of weak winds behind the islands and strong winds on the
islands' flanks. Individual wakes form behind the islands, but
these merge into a broader wake about 240 kilometers (150
miles) to the west. The winds associated with this broader
wake spawn a narrow eastward countercurrent that draws warm
water from west to east. When the winds encounter these warm
surface waters, they rise with convection. Cooler winds move
in to feed the rising air, creating a rotating effect and
reinforcing the current. The current, in turn, helps drive the
winds, setting up a positive feedback between ocean and
atmosphere that continues for thousands of kilometers to the
west.

The study shows that the surface winds react to sea
surface temperature variations as small as a few tenths of one
degree, indicating a climate sensitivity much higher than has
been previously thought. This new knowledge of ocean-
atmosphere interplay will help improve climate models used to
predict phenomena like El Niņo and global warming.

For their paper, Xie and his colleagues used data from
NASA's QuikScat satellite, the European Remote Sensing
satellites and the U.S./Japan Tropical Rainfall Measuring
Mission. The SeaWinds on QuikScat project is managed for
NASA's Earth Science Enterprise by JPL. TRMM is a joint
U.S./Japanese mission managed by NASA's Goddard Space Flight
Center, Greenbelt, MD.

JPL is a division of the California Institute of
Technology in Pasadena.